By active bonnet a bonnet is understood which, in an accident, is lifted automatically by means of one or more actuators, in order to increase the clearance between the bonnet and the heavily deformable components located under it, and thus to provide a longer deformation path for a pedestrian hitting the bonnet. This prevents the risk of the pedestrian hitting the non-deformable vehicle body components, which could lead to life-threatening injuries.
The actuators for such a bonnet can be operated by various means. DE 197 12 961 A1 and DE 103 31 018 A1, for example, describe mechanical, spring-operated actuators. In DE 197 12 961 A1, a pressure spring acts on the body of the vehicle on the one hand, and on the other hand on an elongated hinge carrier, which at one end through a joint and another end through a catch, is anchored to the vehicle body, and which carries a multiple articulated hinge, which a movement causes to open or close the bonnet. A disadvantage of this known mechanical actuator is that it requires powerful and very heavy springs for storing the energy sufficient to rapidly open the bonnet.
A more advantageous weight-to-operational energy ratio can be achieved through using a pneumatic actuator, operated, particularly, on pyrotechnical principles, through the ignition of a propelling charge. However, pyrotechnical actuators have the problem in that the gas pressure used operate them is only available at the moment of lifting the bonnet. In normal operating circumstances, the cylinder of such an actuator is not under pressure, and any play of the piston with respect to the cylinder is transferred to the bonnet itself, when the bonnet is held only by actuators of this type. Hence, constructions with predetermined breaking points are recommended, which, in normal operating conditions, remain intact and hold the bonnet closed securely, but, in a crash or accident, are destroyed, in order to facilitate the raising of the bonnet. The energy required to break the predetermined breaking points must be available at the same time as the energy required for lifting the bonnet, for which purpose a particularly powerful energy source must be provided. In addition to this, the destruction of the constructions with predetermined breaking points leads inevitably to an irreversible damage to the whole construction, with the result that each activation of the actuator requires costly repair work, even when the bonnet lifted by the actuators was not otherwise affected.
For this reason, there is clear demand for a pneumatic actuator for an active bonnet, which has the ability, in normal operating conditions, when it is not under pressure, to provide a solid, play-free connection between the bonnet and the vehicle body. In addition, other demands, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.